A senior UN humanitarian official has called for an immediate pause to the fighting around Syria's contested city of Aleppo so that urgently needed aid can be delivered.

In Geneva, Jan Egeland, adviser to the UN's special envoy to Syria, said the world body was ready to send relief to the city divided between government-controlled and opposition-controlled areas once the fighting pauses.

The last delivery to reach those trapped in rebel-held parts of Aleppo - where the UN estimates some 300,000 residents remain - was in June, he said.

Russia had declared it is offering humanitarian corridors for residents in the area, but rights groups said such passages are not neutral and don't offer guarantees to civilians wishing to use them.

The Britain-based Syrian Observatory for Human Rights reported at least 40 airstrikes on opposition areas of Aleppo and nearby towns, including an attack on a camp for internally displaced Syrians in Atareb.

The Aleppo Media Centre, another activist group, said at least two people were killed in that attack.

Mr Egeland said that in July alone, 44 attacks on hospitals, clinics and health posts around Syria were reported. He added that the UN is hoping at least to "get to a point where we can give coordinates to the parties and not have the hospitals bombed".

Across Syria, Mr Egeland said, the UN was only able to meet 40% of its aid delivery targets for June and July. The UN had hoped to reach 1.2 million people over the last two months.

Rebel fighters have advanced slightly in their attempts to break the siege on Aleppo, seizing new territory in the city's south, the Observatory said. Clashes have been ongoing south of Aleppo since Sunday, when rebels started their counter offensive.